Iphone 7 plus

Since the last update to 11.2.6 the phone is experiencing wifi problems after three to five mins as the phone dosent respond to internet connection whereas in the wifi setting it says it is connected but actually it isn't after refreshing. I have another phone Samsung S8 which works perfectly fine it means there is no issue with the wifi signal during the this period. Kindly fix the issue fast otherwise I will not buy any Apple products in future.